Conventionally, due to acoustic stiffness which a vacant space of a speaker cabinet causes, it has been difficult to realize a loudspeaker system which is compact and capable of reproducing low-pitched sound. As a solution to a problem of the limitation in the low-pitched sound reproduction capability which depends on a cabinet volume, there has been a loudspeaker system in which a block of activated carbon is disposed inside of a cabinet (for example, refer to patent document 1). FIG. 15 is a tectonic profile of a major portion of the loudspeaker system described in the above-mentioned patent document 1.
FIG. 15 is the tectonic profile of the major portion of the loudspeaker system described in the above-mentioned patent document 1. In FIG. 15, the loudspeaker system comprises a cabinet 101, a woofer 102, activated carbon 103, a supporting member 104, a diaphragm 105, and a vent pipe 106. The woofer 102 is attached on a front face of the cabinet 101. The activated carbon 103 is disposed inside of the cabinet 101 in a block-like manner and supported by a back face, a bottom face, an upper face, right and left side faces of the cabinet 101, and the supporting member 104. The supporting member 104 has fine pores formed on an entire surface thereof, through which air passes. The vent pipe 106 is provided on the diaphragm 105 for ventilation between the activated carbon 103 and the woofer 102.
Next, operations of the above-mentioned loudspeaker system will be described. When an electrical signal is applied to the woofer 102, a pressure in the cabinet 101 changes and this pressure vibrates the diaphragm 105. And the vibration of the diaphragm 105 changes a pressure in a vacant space where the activated carbon 103 is disposed. The activated carbon 103 is supported by the supporting member 104 and the cabinet 101 in a block-like manner. Since the supporting member 104 has the fine pores formed on the entire surface thereof, molecules in the air, along with a pressure change caused by the vibration of the diaphragm 105, are absorbed by the activated carbon 103, thereby suppressing the pressure change in the cabinet 101.
As described above, in the conventional loudspeaker system, the cabinet 101 operates as a cabinet which has a large volume, thereby enabling, despite a small size thereof, low-pitched sound reproduction which could be realized if a large cabinet were mounted on a speaker unit. And the vent pipe 106 prevents a pressure change, which is caused by a change in an ambient temperature around the loudspeaker system and a pressure change inside of the loudspeaker system, in a space surrounded by the diaphragm 105, including the activated carbon 103, and the cabinet 101.
On the other hand, as a type of a cabinet which enhances low-pitched sound more than a closed-type cabinet, a bass reflex-type speaker cabinet is used in general. The bass reflex-type loudspeaker system emits low-pitched sound by utilizing acoustic resonance produced by an acoustic volume of the cabinet and an acoustic port provided in the cabinet.    Patent document 1: Japanese translation of PCT international application No. 60-500645